A. Field of the Invention
The present invention relates to lighting fixtures that produce high intensity, controlled, and concentrated light beams for use at relatively distant targets. In particular, the invention relates to such lighting fixtures, their methods of use, and their use in systems where a plurality of such fixtures are used in combination, usually elevated on poles, to compositely illuminate a target area energy-efficiently, with reduced glare and spill light, and with the capability to lower capital and/or operating costs. One primary example is illumination of a sports field.
B. Problems in the Art
Illumination of sports fields is generally called sports lighting. FIGS. 1A-1G illustrate one such sports lighting configuration. Football field 5 of FIG. 1A is illuminated by a set of arrays 1 of light fixtures 2 elevated on poles 6 (see FIG. 1A). As is well known in the art, there are known methods to design the number, type, and position of poles 6 and fixtures 2 to provide a desired or required amount and uniformity of light for the field. There are usually pre-designed lighting quantity and uniformity specifications to follow.
The most conventional form of sports lighting fixture 2 is a several feet in diameter bowl-shaped aluminum reflector with a transparent glass lens 3 suspended from a cross arm 7 fixed to a pole 6 by an adjustable knuckle 4 (see FIG. 1B). Each light fixture 2 has some adjustability both around vertical and horizontal axes. Each fixture 2 can therefore be uniquely aimed relative to the target area or field 5 by adjustment of knuckle 4 relative cross arm 7.
This general configuration of sports lighting fixtures 2 has remained relatively constant over many years because it is a relatively economical and durable design. It represents a reasonable compromise between the desire to economically control high intensity light to a distant target while at the same time minimizing wind load, which is a particularly significant issue when fixtures are elevated out-of-doors to sometimes well over 100 feet in the air. A much larger reflector could control light better. However, the wind load would be impractical. A significant amount of the cost of sports lighting systems involves how the lights are elevated. The more wind load, the more robust and thus more expensive, the poles must be. Also, conventional aluminum bowl-shaped reflectors are formed by a spinning process. Different light beam shapes are needed for different fixtures 2 on poles 6 for different lighting applications. The spinning process for creating aluminum bowl-shaped reflectors is relatively efficient and economical, even for a variety of reflector shapes and light controlling effects. The resistance of aluminum to corrosion is highly beneficial, particularly for outdoors lighting.
Economics plays a big part in most sports lighting. Prime sports lighting customers include entities such as school districts, municipal recreation departments, and private sports leagues. Such entities are particularly sensitive to cost. It would be easier, of course, to meet light quantity and uniformity specifications for a field if one hundred light fixtures on ten poles were erected. The lighting designer could make sure that more than required light is supplied to the field and the volume of space above the field. However, the cost would be prohibitive for most customers. As sports lighting is not usually a necessity, it likely would not be purchased.
Therefore, substantial efforts have gone into reducing sport lighting system costs. One approach is to minimize the number of light fixtures needed to adequately illuminate a target field. Computer programs have been developed towards this end. Programming can optimize the lighting to, in turn, minimize the number of poles and fixtures to meet lighting specifications for an application. Normally, the less light fixtures needed results in lower costs for fixtures but also in lower costs for the poles to elevate the fixtures.
Additional efforts have gone towards developing increasingly more powerful lamps for sports lighting. However, while producing more lumen output, they require more electrical power to operate. More light per fixture may reduce the number of fixtures and poles, but would increase the amount of electrical energy per fixture used. A typical sports light may be used only a couple of hours a day, on average. Several decades, at least, is the expected life of a sports lighting system. Therefore, energy costs become significant, particularly over those lengths of time.
In recent times, sports lighting has also had to deal with the issue of glare and spill light. For example, if light travels outside the area of the sports field, it can spill onto residential houses near the sports field. Also, the high intensity of the lamps can cause glare to such homeowner or create safety issues for drivers on nearby roads. Some communities have enacted laws regulating how much glare or spill light can be caused by sports lighting or other wide-area outdoors lighting. While a number of attempted remedies exist, many result in blocking, absorbing, or otherwise reducing the amount of light going to the field. This can not only increase cost of the lighting system because of the glare or spill control measures, but in some cases requires additional fixtures to meet minimum light quantity and uniformity specifications. More cost might therefore be incurred, to make up for the light lost in glare and spill control measures. In some cases, it can even require more costly and/or additional poles to support the additional fixtures.
Therefore, competing interests and issues provide challenges to sports lighting designers. Some of the interests and issues can be at odds with one another. For example, the need always remains for more economical sports lighting. On the other hand, glare and spill control can actually add cost and/or reduce the amount of light available to light the field. Designers have to balance a number of factors, for example, cost, durability, size, weight, wind load, longevity, and maintenance issues, to name a few. Attempts to advance the art have mainly focused on discrete aspects of sports lighting. For example, computerized design of lighting systems tends to minimize hardware costs and system installation costs but uses conventional lamp and fixture technology, with their weaknesses. Also, larger lumen output lamps produce more light, but are used with conventional fixture technology. A need, therefore, still exists for advancement in the art of sports lighting.
Current wide or large area lighting systems suffer from such things as energy lost in conversion of electricity to light energy; energy lost in the lighting fixture; and energy lost in light going to unintended or non-useful locations. The present invention addresses these issues.